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Abstract:

A seal section for use in a downhole submersible pumping system includes
redundant fluid separation mechanisms. The fluid separation mechanisms
are bag seal assemblies, labyrinth seals, pistons and bellows. The seal
section further includes a shaft, one or more shaft seals and a bag
support tube. An annulus between the shaft and the shaft support tube
provides a fluid flow path from a motor to the fluid separation
mechanisms.

Claims:

1. A seal section for use in a downhole pumping system, the seal section
comprising: a first fluid separation mechanism; and a second fluid
separation mechanism contained within the first fluid separation
mechanism.

2. The seal section of claim 1, wherein the first fluid separation
mechanism is selected from the group consisting of bag seal assemblies,
labyrinth seals, pistons and bellows.

3. The seal section of claim 2, wherein the second fluid separation
mechanism is selected from the group consisting of bag seal assemblies,
labyrinth seals, pistons and bellows.

4. The seal section of claim 1, wherein the first fluid separation
mechanism is an exterior bag seal assembly and the second fluid
separation mechanism is an interior bag seal assembly.

5. The seal section of claim 4, wherein the interior bag seal assembly
comprises a first check valve in communication with the exterior bag seal
assembly.

6. The seal section of claim 5, wherein the exterior bag seal assembly
comprises a second check valve in communication with the wellbore.

7. The seal section of claim 4, wherein the exterior bag seal assembly
and the interior bag seal assembly are connected in a series
configuration.

8. The seal section of claim 4, wherein the exterior bag seal assembly
and the interior bag seal assembly are connected in a parallel
configuration.

9. The seal section of claim 1, wherein the first fluid separation
mechanism is a bag seal assembly and the second fluid separation
mechanism is a labyrinth seal.

10. The seal section of claim 9, wherein the labyrinth seal comprises: a
labyrinth chamber; inlet ports connected to the labyrinth chamber; outlet
ports connected between the labyrinth chamber and the bag seal assembly;
and a cap.

11. The seal section of claim 1, wherein the first fluid separation
mechanism is a labyrinth seal and the second fluid separation mechanism
is a bag seal assembly.

12. The seal section of claim 1 wherein the first fluid separation
mechanism is an external labyrinth seal and the second fluid separation
mechanism is an internal labyrinth seal.

13. A seal section for use in a submersible pumping system, the seal
section comprising: a shaft; a bag support tube surrounding the shaft; an
annulus between the shaft and the bag support tube; a first fluid
separation mechanism; a second fluid separation mechanism contained
within the first fluid separation mechanism; and at least one shaft seal
along the shaft contained within the first fluid separation mechanism.

14. The seal section of claim 13, wherein the first fluid separation
mechanism is selected from the group consisting of bag seal assemblies
and labyrinth seals.

15. The seal section of claim 14, wherein the second fluid separation
mechanism is selected from the group consisting of bag seal assemblies
and labyrinth seals.

16. The seal section of claim 13, wherein the first fluid separation
mechanism is an exterior bag seal assembly and the second fluid
separation mechanism is an interior bag seal assembly.

17. The seal section of claim 16, wherein the shaft seal diverts fluid
from the annulus into the interior bag seal assembly.

18. A pumping system for deployment in a subterranean well, the pumping
system comprising: a motor; a pump driven by the motor; and a seal
section between the motor and the pump, wherein the seal section
comprises: a first fluid separation mechanism; and a second fluid
separation mechanism contained within the first fluid separation
mechanism.

19. The pumping system of claim 18, wherein the first fluid separation
mechanism is selected from the group consisting of bag seal assemblies
and labyrinth seals.

20. The pumping system of claim 18, wherein the second fluid separation
mechanism is selected from the group consisting of bag seal assemblies
and labyrinth seals.

[0002] This invention relates generally to the field of submersible
pumping systems, and more particularly, but not by way of limitation, to
an improved seal section.

BACKGROUND

[0003] Submersible pumping systems are often deployed into wells to
recover petroleum fluids from subterranean reservoirs. Typically, the
submersible pumping system includes a number of components, including one
or more fluid filled electric motors coupled to one or more high
performance pumps. Each of the components and sub-components in a
submersible pumping system is engineered to withstand the inhospitable
downhole environment, which includes wide ranges of temperature, pressure
and corrosive well fluids.

[0004] Components commonly referred to as "seal sections" protect the
electric motors and are typically positioned between the motor and the
pump. In this position, the seal section provides several functions,
including transmitting torque between the motor and pump, restricting the
flow of wellbore fluids into the motor, protecting the motor from axial
thrust imparted by the pump, and accommodating the expansion and
contraction of motor lubricant as the motor moves through thermal cycles
during operation. Prior art seal sections employ a single seal bag,
bellows or labyrinth chamber to accommodate the volumetric changes and
movement of fluid in the seal section while providing a positive barrier
between clean lubricant and contaminated wellbore fluid.

[0005] While generally acceptable, prior art seal sections often fail to
isolate contaminated well fluids from clean lubricants. As wellbore
fluids are drawn into the seal section, sand and other particulate solids
may accumulate and compromise the integrity of the seal mechanism within
the seal section. Accordingly, there exists a need for an improved design
that is more resistant to contamination and wear caused by solid
particles. It is to this and other deficiencies in the prior art that the
present invention is directed.

SUMMARY OF THE INVENTION

[0006] In exemplary embodiments, a seal section for use in a downhole
submersible pumping system includes redundant fluid separation
mechanisms. The fluid separation mechanisms are selected from the group
consisting of bag seal assemblies, labyrinth seals, pistons and bellows.
The seal section may further include a shaft, one or more shaft seals and
a bag support tube. An annulus between the shaft and the shaft support
tube provides a fluid flow path from a motor to the fluid separation
mechanisms. In another aspect, the embodiments of the seal section are
incorporated within a downhole pumping system

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is an elevational view of a submersible pumping system
constructed in accordance with exemplary embodiments.

[0008] FIG. 2 is a cross-sectional view of a seal section for use with the
submersible pumping system of FIG. 1.

[0009] FIG. 3 is a cross-sectional view of a seal section for use with the
submersible pumping system of FIG. 1.

[0010] FIG. 4 is a cross-sectional view of a seal section for use with the
submersible pumping system of FIG. 1.

[0011] FIG. 5 is a cross-sectional view of a seal section for use with the
submersible pumping system of FIG. 1.

DETAILED DESCRIPTION

[0012] In accordance with an exemplary embodiment, FIG. 1 shows an
elevational view of a pumping system 100 attached to production tubing
102. The pumping system 100 and production tubing 102 are disposed in a
wellbore 104, which is drilled for the production of a fluid such as
water or petroleum. As used herein, the term "petroleum" refers broadly
to all mineral hydrocarbons, such as crude oil, gas and combinations of
oil and gas. The production tubing 102 connects the pumping system 100 to
a wellhead 106 located on the surface. Although the pumping system 100 is
primarily designed to pump petroleum products, it will be understood that
the pumping system 100 can also be used to move other fluids. It will
also be understood that, although each of the components of the pumping
system 100 are primarily disclosed in a submersible application, some or
all of these components can also be used in surface pumping operations.

[0013] The pumping system 100 includes a combination of a pump assembly
108, a motor assembly 110 and a seal section 112. The motor assembly 110
is an electrical motor that receives power from a surface-mounted motor
control unit (not shown). When electrically energized, the motor assembly
110 drives a shaft that causes the pump assembly 108 to operate. The seal
section 112 shields the motor assembly 110 from mechanical thrust
produced by the pump assembly 108 and provides for the expansion of motor
lubricants during operation. The seal section 112 also isolates the motor
assembly 110 from the wellbore fluids passing through the pump assembly
108. Although only one of each component is shown, it will be understood
that more can be connected when appropriate. It may be desirable to use
tandem-motor combinations, multiple seal sections, multiple pump
assemblies or other downhole components not shown in FIG. 1. For example,
in certain applications it may be desirable to place a seal section or
pressure compensating chamber 112 below the motor assembly 110.

[0014] Referring now to FIG. 2, shown therein is a cross-sectional view of
the seal section 112. The seal section 112 includes a housing 114, a
shaft 116, and a plurality of fluid separation mechanisms 118. The shaft
116 transfers mechanical energy from the motor assembly 110 to the pump
assembly 108. The housing 114 is configured to protect the internal
components of the seal section 112 from the exterior wellbore
environment. The seal section 112 further includes a plurality of shaft
seals 120 that prevent the migration of fluid along the shaft 116. In
some embodiments, the shaft seals 120 are mechanical seals or
spring-biased lip seals. In the embodiment depicted in FIG. 2, there are
two shaft seals 120a, 120b in the seal section 112.

[0015] In the embodiment depicted in FIG. 2, the fluid separation
mechanisms 118 include an interior bag seal assembly 122 and an exterior
bag seal assembly 124. The interior bag seal assembly 122 is contained
within the exterior bag seal assembly 124, which is in turn contained
within the housing 114. The interior bag seal assembly 122 and exterior
bag seal assembly 124 are each supported by a bag support tube 126 that
surrounds the shaft 116. The space between the exterior of the shaft 116
and the interior of the bag support tube 126 provides an annulus 128
through which fluids can pass.

[0016] The interior bag seal assembly 122 includes a first seal bag 130,
fluid ports 132 and one or more first check valves 134. In some
embodiments, the first seal bag 130 is constructed from a durable
material. Suitable materials include fluoropolymers and highly saturated
nitrile rubber. The fluid ports 132 place the interior of the first seal
bag 130 in communication with the annulus 128. The first check valve 134
is in fluid communication with the annulus 128 and also the interior of
the exterior bag seal assembly 124. The first check valve 134 is biased
in a closed position. When a predetermined threshold pressure is applied
to the first check valve 134, the first check valve 134 opens and allows
fluid from the annulus 128 to pass into the exterior bag seal assembly
124.

[0017] The exterior bag seal assembly 124 includes a second seal bag 136,
fluid ports 138 and a second check valve 140. In exemplary embodiments,
the second seal bag 136 is constructed from a durable material. Suitable
materials include fluoropolymers and highly saturated nitrile rubber. The
fluid ports 138 place the interior of the second seal bag 136 in
communication with the annulus 128. The second check valve 140 is in
fluid communication with the annulus 128 above the shaft seal 120a and
also directly, or indirectly through the pump 108, with the wellbore 104.
The second check valve 140 is biased in a closed position. When a
predetermined threshold pressure is applied to the second check valve
140, the second check valve 140 opens and allows fluid from the annulus
128 to pass into the space around the exterior of the second seal bag
136, above the shaft seal 120a, and into the wellbore 104 or pump 108.

[0018] During use, fluid from the motor 110 migrates up the shaft 116 in
the annulus 128 to fluid ports 132. The shaft seal 120a prevents the
fluid from passing further along the annulus 128 and the fluid passes
through the fluid ports 132 into the interior of the first seal bag 130.
As the first seal bag 130 expands to accommodate the fluid, the pressure
inside the first seal bag 130 increases. At the point at which the
pressure inside the first seal bag 130 exceeds the threshold pressure for
the first check valve 134, the first check valve 134 temporarily opens to
allow fluid to pass through to the interior of the second seal bag 136.
Once the pressure has been relieved the first check valve 134 closes.
Over time, the fluid in the second seal bag 136 may accumulate to a point
at which the pressure inside the second seal bag 136 exceeds the
threshold pressure for the second check valve 140. At that point, the
second check valve 140 opens and fluid from the second seal bag 136
travels through the fluid ports 138 into the annulus 128, through the
open second check valve 140, into the space around the exterior of the
second seal bag 136 and into the wellbore 104 or pump 108.

[0019] As depicted in FIG. 2, the first seal bag 130 and second seal bag
136 operate in series. Fluid must pass through the first seal bag 130
before it can pass into the second seal bag 136. In an alternative
embodiment, the shaft seal 120a is removed and fluid is allowed to pass
through the annulus 128 between the first seal bag 130 and the second
seal bag 136. In this configuration, the first seal bag 130 and the
second seal bag 136 operate in a parallel configuration to provide
additional seal volume, without the redundancy of the fluid separation
mechanisms 118 operating in a serial configuration.

[0020] Turning to FIG. 3, shown therein is another embodiment of the seal
section 112. In the embodiment depicted in FIG. 3, the seal section 112
includes two fluid separation mechanisms 118 that include a labyrinth
seal 142 contained within a seal bag assembly 144. The internal labyrinth
seal 142 includes a labyrinth chamber 146, inlet ports 148, outlet ports
150 and a cap 152. The inlet ports 148 provide a fluid flow path from a
lower annulus 128a to the labyrinth chamber 146. The outlet ports 150
provide a fluid path from the labyrinth chamber 146 to the seal bag
assembly 144. The cap 152 and shaft seal 120a prevent fluid from
bypassing the labyrinth seal 142 along the annulus 128.

[0021] The seal bag assembly 144 includes a seal bag 154, discharge ports
156 and a check valve 158. In some embodiments, the seal bag 154 is
constructed from a durable material. Suitable materials include
fluoropolymers and highly saturated nitrile rubber. The interior of the
seal bag 154 is placed in fluid communication with the check valve 158
through the discharge ports 156 and upper annulus 128b. The check valve
158 is configured to provide one-way flow in response to a fluid pressure
in excess of a predetermined threshold pressure.

[0022] During use, fluid travels up the shaft 116 inside the lower annulus
128a into the labyrinth seal 142. The fluid is forced through inlet ports
148 into the labyrinth chamber 146. Solids and other particulates are
trapped at the bottom of the labyrinth chamber 146. Fluid is discharged
from the labyrinth chamber 146 through the outlet ports 150 into the
interior of the seal bag 154. When the pressure inside the seal bag 154
exceeds the predetermined threshold pressure of the check valve 158, the
check valve 158 temporarily opens and fluid from the seal bag 154 is
expelled through the discharge ports 156, upper annulus 128b and check
valve 158 into the wellbore 104 or the pump 108.

[0023] Turning to FIG. 4, shown therein is yet another embodiment of the
seal section 112. In the embodiment depicted in FIG. 4, the seal section
112 includes two fluid separation mechanisms 118 that include a seal bag
assembly 160 contained within a labyrinth seal 162. The seal bag assembly
160 includes a seal bag 164, fluid ports 166 and a check valve 168. The
fluid ports 166 place the interior of the seal bag 164 in fluid
communication with the annulus 128 between the bag support tube 126 and
shaft 116. In some embodiments, the seal bag 164 is constructed from a
durable material. Suitable materials include fluoropolymers and highly
saturated nitrile rubber. The check valve 168 is configured to provide
one-way flow in response to a fluid pressure in excess of a predetermined
threshold pressure. The shaft seal 120a prevents fluid from bypassing the
check valve 168.

[0024] The labyrinth seal 162 includes an internal chamber 170, an
external chamber 172, exchange ports 174, a discharge tube 176 and a
division wall 178. The internal chamber 170 is defined by the annular
space between division wall 178 and the seal bag 164. The external
chamber 172 is defined by the annular space between the outside of the
divisional wall 178 and the inside of the housing 114. The exchange ports
174 are positioned near the top of the division wall 178 and place the
internal chamber 170 in fluid communication with the external chamber
172. The discharge tube 176 extends to the bottom of the external chamber
172 and places the external chamber 172 in fluid communication with the
wellbore 104 or pump 108.

[0025] During use, fluid migrates along annulus 128 between the shaft 116
and the bag support tube 126 to seal bag 164 through the fluid ports 166.
When the pressure of the fluid in the seal bag 164 exceeds the threshold
pressure of the check valve 168, the check valve 168 temporarily opens
and fluid is expelled from the seal bag assembly 160 into the labyrinth
seal 162. As the fluid enters the internal chamber 170, solids are drawn
by gravity to the bottom of the internal chamber 170 and clean fluid is
allowed to pass through the exchange ports 174 into the external chamber
172. From the external chamber 172, fluids are allowed to pass through
the discharge tube 176 into the wellbore 104 or pump 108.

[0026] Fluids from the wellbore 104 may be drawn into the seal section 112
through the discharge tube 176. Solid particles in fluids passing through
the discharge tube 176 into the external chamber 172 are trapped at the
bottom of the external chamber 172 before the fluid passes into the
internal chamber 170. Remaining solid particles are trapped within the
bottom of the internal chamber 170.

[0028] The first labyrinth chamber 184 is defined by the annular space
between the division wall 186 and the exterior of the labyrinth support
tube 183. The second labyrinth chamber is defined by the annular space
between the exterior of the division wall 186 and the interior of the
outer wall 190. The inlet ports 192 extend through the labyrinth support
tube 183 and place the first labyrinth chamber 184 in fluid communication
with the annulus 128. The lower fluid exchange ports 194 extend through
the division wall 186 near the bottom and place the first labyrinth
chamber 184 in fluid communication with the second labyrinth chamber 188.
The discharge ports 196 extend through the top of the outer wall 190 and
place the second labyrinth chamber 188 in fluid communication with the
external labyrinth seal 182.

[0029] The external labyrinth seal 182 is contained within the housing 114
and includes an external labyrinth chamber 198 and a discharge tube 200.
The external labyrinth chamber 198 is defined as the annular space
between the interior of the housing 114 and the exterior of the outer
wall 190 of the internal labyrinth seal 180. The discharge tube 200
extends downward toward the bottom of the external labyrinth chamber 198.
The shaft seal 120a prevents fluid from bypassing the internal labyrinth
seal 180 and external labyrinth seal 182.

[0030] During a heating cycle, fluid enters the internal labyrinth seal
180 from the annulus 128 through inlet ports 192. Fluid is passed through
the inlet ports 192 into the first labyrinth chamber 184, through the
lower fluid exchange ports 194 into the second labyrinth chamber 184 and
through the discharge ports 196 into the external labyrinth chamber 198
of the external labyrinth seal 182. From the external labyrinth chamber
198, fluid travels through the discharge tube 200. The redundant internal
labyrinth seal 180 and external labyrinth seal 182 extends the useful
life of the seal section 112 by ensuring that contaminates and solid
particles are trapped within the external labyrinth chamber 198, second
labyrinth chamber 188 and first labyrinth chamber 184.

[0031] Although the internal and external fluid separation mechanisms 118
have been disclosed as incorporating bag seal assemblies and labyrinth
seals, it will be appreciated that other sealing mechanisms are employed
in other embodiments. It may be desirable to use piston seals and bellows
for one or both of the internal and external fluid separation mechanisms
118. For example, in one embodiment, the seal section 112 includes a
movable piston seal for the internal fluid separation mechanism 118 and a
bag seal assembly for the external fluid separation mechanism 118. In
another embodiment, the internal fluid separation mechanism 118 includes
an accordion-fold bellows seal that expands and contracts along a
longitudinal axis within an external fluid separation mechanism 118 that
includes a radially expanding bag seal assembly.

[0032] Thus, in various embodiments, the seal section 112 includes an
internal fluid separation mechanism 118 contained within an external
fluid separation mechanism 118, which is in turn contained within the
housing 114. The internal fluid separation mechanism 118 is selected from
bag seal assemblies, labyrinth seals, pistons and bellows. Likewise, the
external fluid separation mechanism 118 is selected from bag seal
assemblies, labyrinth seals, pistons and bellows. The internal and
external fluid separation mechanisms 118 may be connected in series or
parallel by modifying the flow path through the seal section 112.

[0033] It is to be understood that even though numerous characteristics
and advantages of various embodiments of the present invention have been
set forth in the foregoing description, together with details of the
structure and functions of various embodiments of the invention, this
disclosure is illustrative only, and changes may be made in detail,
especially in matters of structure and arrangement of parts within the
principles of the present invention to the full extent indicated by the
broad general meaning of the terms in which the appended claims are
expressed. It will be appreciated by those skilled in the art that the
teachings of the present invention can be applied to other systems
without departing from the scope and spirit of the present invention.